LeetCode 92. Reverse Linked List II

原题网址：https://leetcode.cn/problems/reverse-linked-list-ii/

给一个链表,Flip the nodes in an interval.

Find the previous node of the left interval,Then start deleting nodes,until out of range;Finally splicing the flipped linked list and the remaining linked list;

    public ListNode reverseBetween(ListNode head, int left, int right) {
    
        if(head == null || head.next == null || left == right) {
    
            return head;
        }
        // 如果left是第一个数据,Unable to find its predecessor,So refer to the virtual node
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        // By finding the previous node,删除left节点
        ListNode prev = null;
       
        ListNode first = null;
        ListNode tail = null;


        ListNode cur = dummyHead;

        for(int i=0;i<right;i++) {
    
            // 找到left的前一个节点了,开始删除.
            if(i>=left-1) {
    
                prev = cur;
                ListNode node = prev.next;
                prev.next = node.next;

                if(first == null) {
    
                    first = tail = node;
                } else {
    
                    node.next = first;
                    first = node;
                }

            } else {
    
                cur = cur.next;

            }
        }
   

        tail.next = prev.next;
        prev.next = first;
        return dummyHead.next;

    }